1. Field of the Invention
The present invention relates to a rotary damper intervening between two members for generating a rotational resistance when relatively rotating one member with respect to the other member.
2. Description of the Related Art
A rotary damper is intervened between relatively rotating members in order to generate a rotational resistance and to realize heavy motions in such cases as adjusting an angle of a reclining seat, folding a folding seat, folding out or folding a retractable ottoman, opening or closing a hinged door, or opening or closing a lid of apparatuses. The rotary dampers are classified according to operating principles. For example, a rotary damper generating a rotational resistance by utilizing a viscosity resistance of a viscose fluid is known (hereafter sometimes referred to as “viscose fluid utilizing rotary damper”). As for the viscose fluid utilizing rotary damper, one having high functionality such as changing the rotational resistance depending on a rotational direction is proposed (for example, JP 2011-190917 A). However, since the viscose fluid utilizing rotary damper requires high liquid-tight performance, each member configuring the viscose fluid utilizing rotary damper requires high accuracy of dimension. Therefore each member configuring the viscose fluid utilizing rotary damper is normally manufactured by die casting. The viscose fluid utilizing rotary damper has a defect in that when setting the rotational resistance, it is needed to make a new die. This makes a development and design period longer and a manufacturing cost higher. In addition, the viscose fluid utilizing rotary damper has a defect in that it is difficult to downsize and weight save.
A rotary damper having a brake spring configured by a coil spring which is externally fitted to a brake drum with the coil spring tightened is also known (for example, JP11-002278A). This rotary damper generates the rotational resistance by a friction between the brake spring and an outer periphery of the brake drum (hereafter this rotary damper sometimes referred to as “coil spring utilizing rotary damper”). According to the coil spring utilizing rotary damper, the rotational resistance is changed by adjusting coil turns of the brake spring or a position to which ends of the brake spring is fixed. In addition, it is easy to downsize and weight save. However, in case an overmuch load is applied, the brake spring possibly permanently deforms (especially around its ends) in the coil spring utilizing rotary damper. In addition, the coil spring utilizing damper changing the rotational resistance depending on a rotational direction is not found. In relation to this, JP 2010-142439 A discloses an angle adjustable head rest configured to generate different resistance depending on the rotational direction by adapting a coil spring having a small diameter portion at one end and large diameter portion at the other end. However, this coil spring is for locking the head rest at a predetermined angle, but it is not for the rotary damper.
Present invention solves above mentioned problems, makes it possible to set the rotational resistance with an easy adjustment and provides the coil spring utilizing rotary damper easy to downsize, weight save and reduce cost. Present invention also provides the coil spring utilizing rotary damper in which the brake spring does not permanently deform by a prolonged use. Further, present invention provides the coil spring utilizing damper in which complicated functions such as changing the rotational resistance depending on the rotational direction are easy to realize.